JP2000091639A - Light emitting element provided with reflecting contact section carrying fine pattern and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element which can uniformly emit light having a sufficient luminous intensity. SOLUTION: A light emitting element has contact sections 18 and 20 which are respectively provided correspondingly to an n-type layer 12 and a p-type layer 16. The top-side contact section 20 has an opening patterned by etching, annealing, etc. Since the light emitted from the light emitting layer of the light emitting element is emitted through the opening of the contact section 20, uniform light mission is guaranteed from the light emitting element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement relating to light extraction or light extraction from a light emitting device.

[0002]

2. Description of the Related Art Light extraction from semiconductor light emitting devices (LEDs) is limited by the high optical refractive index of semiconductor materials relative to that of the surrounding environment. For example, the optical refractive index n of a semiconductor material is about 2.2 to 3.8, while the optical refractive index n of air is about 1, and the optical refractive index n of a transparent epoxy is n.
Is about 1.5. The amount of extraction depends on the micro-geometry of the LED and the light generated in the active area or light-emitting layer.
It largely depends on the dimensional emission characteristics. Most of the light generated within a light emitting device is attenuated before it can be extracted to the outside, due to absorption by surrounding materials such as, for example, epitaxial layers, confinement regions, substrates, die attach materials, and electrical contacts.

A typical light emitting device generates photons emitted in a wide range of directions at a pn junction (ie, achieves substantially isotropic light emission). As a result, most of the emitted light is emitted from the semiconductor, and is incident on the light emitting element / external environment interface at an angle exceeding the critical angle. Since these light rays are reflected inward, they are easily affected by absorption in the light emitting device. For a typical GaN-based LED, only about 11% of the photons are incident on the top surface within the critical angle (especially for transmission into the epoxy). The remaining light reflects inward at least once before exiting the chip.

[0004] Inwardly reflected light in AlInGaN LEDs is particularly susceptible to absorption by the p-layer contact. Since no current can flow laterally through the semiconductor layer, these contacts must cover substantially the entire pn junction light emitting region. A p-type epitaxial layer typically has a sheet resistance greater than 20,000 ohms / square and has a very low electrical conductivity, so that the current is directly below the metal at the contact or about 1 μm from the edge of the contact.
Will be confined within

In order to enable light to be extracted, AlIn
GaN LEDs utilize p-type layer contacts made of very thin layers. This is typically 50-500 mm thick
And made from AuNi or a similar alloy. These thin "semi-transparent" layers transmit most of the nearly normally incident light, but typically absorb more than 20% of this light.

There are several problems with translucent contacts. First, the contacts absorb most of the LED emission. Translucent contacts can transmit as much as about 80% of light at near normal incidence, but produce relatively large absorption above a critical angle (where light can be extracted from the LED). Most of the light emitted by LED light
Reflecting inwardly will result in multiple hits with partially absorbing contacts. For LEDs fabricated on a sapphire substrate, about 70% of the emitted light is captured between the absorbing metal surface and the substrate. The metal at the contact rapidly attenuates the intensity of this light, so that the translucent metal film may absorb most of the emitted light.

A second problem is that since the semi-transparent metal thin film is extremely thin, on the order of several hundred angstroms, the thin film does not completely cover the rough semiconductor surface. This is particularly disadvantageous in view of improving light extraction by rough surfaces. The translucent thin film may not conduct current uniformly over a rough, ie, uneven surface, and may be discontinuous. For this reason, unevenness occurs in light emission by the LED.
That is, the element does not partially emit light.

A third problem with thin metals is that they are susceptible to scratching, which can result in discontinuous conductive surfaces. For this reason, handling becomes difficult and LED
Manufacturing process becomes complicated.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light emitting device or LED capable of guaranteeing uniform light emission. Furthermore, the present invention relates to a light emitting device or L
It is another object to provide a method for manufacturing an ED.

[0010]

SUMMARY OF THE INVENTION The present invention provides an AlInGaN light emitting device that includes a finely patterned reflective p-type contact that enhances light extraction efficiency. Since these contacts include rows of closely spaced openings,
Light can pass through them. Thus, light incident on the contact will either pass through the aperture or be reflected back to the LED with very little loss. For this reason, the absorption of light generated in the conventional translucent contact portion is greatly reduced. This contact can be realized with a thick, highly conductive metal, thus reducing the current spreading resistance (even on rough semiconductor surfaces). The contact metal openings occupy 20-80% of the total contact area and are closely spaced to achieve transparency and uniform light emission. The contacts are made of a highly reflective material such as Ag, Al or Rh. This ensures that light transmitted through the contact is reflected with very little absorption. An additional dielectric encapsulation material such as, for example, silicon dioxide, silicon nitride, aluminum nitride, or aluminum oxide can be deposited over the p-type layer contact. If selected, the surface of the active region can be roughened or textured by an etching process that is self-aligned with the metal opening. These features scatter the light reflected inward, increasing the probability of light extraction. By attaching a reflective layer to the bottom surface of the LED, light extraction efficiency is further improved.

[0011]

DETAILED DESCRIPTION A typical GaN-based LED includes a heterojunction structure with a light emitting layer sandwiched between an n-type layer and a p-type layer. The p-type layer contact is electrically connected to the p-type layer, while the n-type layer contact is electrically connected to the n-type layer. FIG. 1 shows an embodiment of the invention, according to which it is manufactured on a substrate 8,
Heterojunction device 10 with light emitting layer 14 interposed between n-type layer 12 and p-type layer 16 is shown. A reflector 9 is arranged on the back of the substrate 8. The n-type layer contact 18 is electrically connected to the n-type layer 12, while the p-type layer contact 2
0 is electrically connected to the p-type layer 16. Preferably, both electrical contacts 18, 20 are made of a reflective metal, i.e. a metal that reflects more than 70% of normal incident visible light.
The p-type layer bonding pad is disposed on the p-type layer contact portion.

According to the present invention, the p-type layer contact portion 20 includes:
Included are apertures in a finely spaced pattern that allow light to pass through the contacts. The dimensions of the openings must be small so that the pn junction can (at least partially) conduct current in the openings. In order to ensure that light can pass through the contact, the size of the opening must be greater than about ４ of the wavelength λ of visible light in the material system. For example, λ of visible light in the air is in a range of 400 to 700 nm. Λ in GaN ranges from 160 to 285 nm. Preferably, the smallest dimension of the opening may be at least 160 nm.

The desired size of the opening is determined by the current flowing through the p-type layer 16. For the pn junction 14 to emit light just below the opening, current must flow from the edge of the metal to the junction region below the opening. Therefore, it is desirable that its minimum dimension be approximately the same as the distance the current flows laterally through the LED. Typical A
lInGaN devices have a thickness of 0.25 to 0.5 μm.
m and the sheet resistance is greater than 20,000Ω / □
It has a mold layer. Thus, the current spreads from the edge of the contact by less than about 1 μm. Since the current flows from the contact metal on all sides of the opening, the preferred minimum dimension of the opening is 0.5 to 2 μm.
Experimental devices were manufactured such that the thickness of the p-type layer was greater than 1 μm. For these diodes, a desirable minimum dimension is 1 to 4 μm. The aperture should be as large as possible to allow the passage of light and to facilitate manufacture. However, the opening should not be larger than the range in which the current flows in the lateral direction.
Otherwise, the area of the LED is wasted, resulting in "unevenness" in the light emitting pattern of the LED.

The shape of the openings can be a regular pattern such as circles, squares, grid lines, or honeycombs, or any other shape. The metal must be connected continuously around the opening. The opening of the metal contact preferably occupies 20 to 80% of the area of the contact. Below 20%, the contact will not transmit enough light. According to this, the photons are easily captured by the LED and re-absorbed. If it exceeds 80%, the amount of the metal becomes insufficient, and it becomes impossible to uniformly spread the current by using the metal contact having the shape and dimensions that can be easily manufactured.

The metal of the p-type layer contact portion is, for example, 1,000
Thick layers, such as 0 to 30,000 degrees, are desirable. This assures that the contacts can spread the current through the device with little resistance and effectively cover the surface topography on the wafer. Alternatively, the metal to be patterned can be thin enough to be translucent. In this case, the efficiency of the device is improved by the present invention,
The benefits of thicker metallization (such as the ability to conduct over a rough surface) are not realized. The conductive material is a reflective metal, preferably silver, aluminum, rhodium, an alloy of Ag, Al, Rh, or Ag, Al, Rh, which makes the reflectivity of the contact portion greater than 70%. It is desirable to have such a multilayer contact portion. The contacts can be made from relatively low-reflectivity metals such as NiAu, Pd, TiPt, but the LEDs made in this way are less efficient.

The preferred p-type layer contact is a "perforated" silver mesh formed by etching holes in the row of openings in Ag. Silver is used because it has the highest reflectance among metals and can realize low-resistance ohmic contact with the p-type layer of GaN. The bonding pads for the n-type and p-type layers are made of Al, which has high reflectivity (about 90%), good adhesion to GaN, and good adhesion to n-type GaN. This is because a low-resistance contact portion can be formed.

In all embodiments, light incident on the top surface of the LED strikes either the highly reflective metallic or non-metallic portions of the device. When light hits a non-metallic part, it escapes from the chip or reflects inward without attenuation. When hitting the mirror portion, the light reflects inward with minimal attenuation. This light
Scattered into the device and escape from the side of the device,
Or, it is incident on the top surface again. Since there is minimal attenuation, light can be reflected many times, increasing the probability of exiting the chip. Thus, although the top surface is partially obscured or obscured by darkening, the thicker semi-continuous metal film improves light extraction from the LED.

In general, LEDs are designed so that opaque contacts (or contact pads) are as small as possible to minimize the degree or obscuration of the chip surface. The present invention is significantly different from the prior art.
In the case of the present invention, light extraction is masked because the reflectivity of the ohmic contacts is high, the substrate has a reflective coating on the back, and the epitaxial material and the substrate do not strongly absorb the emitted light. It is improved despite the large hidden area. Therefore, the light travels many times in the chip, so that there is a high probability that the light will escape without being absorbed.

Since the finely patterned contacts can be much thicker than the translucent metal, the sheet resistance of the contact layer is also reduced. This assures that the contacts of the device will not be current crowded. If the contact is relatively thick,
Rough or uneven surfaces are also effectively coated. As a result, it is possible to improve light extraction by intentionally roughening the semiconductor surface. Under wider conditions, it is also possible to grow epitaxial LED thin films. In particular, layers grown after the pn junction can be grown at temperatures below 1000 ° C. This growth temperature range minimizes thermal damage to the active region that can occur during growth, but is rough or uneven, such that thin metallization or coating with a metal film is not easy. Will result in a surface.

FIG. 2 shows a flowchart of a process for manufacturing the contact portion. In step 100,
A reflective material is deposited on the p-type layer of the LED. Step 11
At 0, the device is annealed. In step 120,
A resist is deposited and exposed to form an opening pattern. In step 130, for the metal of the contact portion,
If selected, the epitaxial layer of the LED is subjected to an etching process to further configure the pattern. The etching process can be performed by chemical etching, ion milling, reactive ion etching, or the like. In step 140, the resist is removed. In step 150,
An additional dielectric encapsulation material is deposited over the contacts.

Another method of forming the opening is to anneal the contact at an elevated temperature. Under appropriate conditions, surface tension will cause openings in the metal. For example, a layer of silver with a thickness of 1000
The surface of GaN is heated and dehumidified by annealing, and after annealing for several minutes, a parallel or mesh-like opening space or opening portion is formed.

FIG. 3 shows an LE manufactured according to the present invention.
D and output power as a function of drive current are contrasted for LEDs fabricated with conventional AuNi translucent contacts. LEDs fabricated with finely patterned Ag contacts are 1.5 to 2 times more efficient at all currents than prior art LEDs.

FIG. 4 shows a second preferred embodiment. The top surface is sealed with a dielectric material having a refractive index of more than 1.5, such as aluminum oxide, silicon nitride, aluminum nitride, hafnium oxide, or titanium oxide. If the refractive index of the dielectric layer 22 is higher than the refractive index of the epoxy surrounding the LED, the probability that light can pass through the openings in the silver layer increases. The encapsulation material allows for inward reflection of light on the upper side of the silver mirror rather than below. This increases the probability of light exiting without attenuation. Further, the encapsulant improves the adhesion between the metal thin film and the LED surface by intersecting the thickness in the opening space over the entire surface and supporting the metal at the opening. This is particularly advantageous when the contacts are made of silver. The dielectric further protects the metal layer from scratches that may occur during manufacturing and protects it from environmental degradation, for example, oxidation or discoloration.

FIG. 5 shows a third preferred embodiment. The top surface of the LED is roughened, preferably so as to be aligned with the contact opening. This is the same lithography process used to form the pattern of the contact portion.
This can be realized by etching N. The hole or opening to be etched can extend into the p-type layer 20 or can reach the same depth as the substrate 8. The roughened surface scatters light within the semiconductor layer (otherwise light will be trapped due to inward total internal reflection).
Some of the light is reflected toward the exit angle, resulting in higher extraction efficiency from the LED.

The AlInGaN device can also include an alloy of AlInGaN using phosphorus or arsenic instead of a portion of nitrogen. The reflective contact with the fine pattern formed is a vertical geometrically arranged AlInGaN
An LED, for example comprising a p-type layer contact on one side of the chip,
It can also be used for LEDs having an n-type layer contact on the other side. The present invention can also be used at the rough-finished substrate / epitaxial layer interface, for example, by using a substrate that has been intentionally rough-finished or roughened to scatter light before GaN growth. It is possible.

As explained by the above embodiments, the present invention comprises an n-type layer (12), a p-type layer (16), and a visible light interposed between the n-type layer and the p-type layer. AlInGaN including a light emitting layer (14) serving to emit λ
A heterojunction device (10), which is a device, and an n-type layer contact portion (18) connected to the n-type layer on one side;
The other is a p-type layer contact portion (2) connected to the p-type layer.
0), two contacts (18, 2
0), wherein at least one of the two contact portions (18, 20) includes a patterned opening having a minimum dimension of λλ, and emits light through the opening. The present invention provides a light-emitting element characterized by being capable of:

Preferably, the opening forming the pattern has a top surface area of 20 to 80 of the p-type layer contact portion (20).
%.

Preferably, the two contact portions (18, 2
At least one of 0) is a reflective metal having a normal incidence reflectance of greater than 70%.

Preferably, the material forming the p-type layer contact portion (20) is selected from a group including Ag, Al, Rh, and an alloy of Ag, Al and Rh.

Preferably, the material forming the p-type layer contact portion (20) is a multilayer contact portion containing the reflective metal, and the reflective metal is made of Ag, Al, and Rh.
Is selected from the group containing

Preferably, the heterojunction device (1)
0) has a rough surface including a specific uneven structure under at least one of the two contact portions (18, 20) having the openings forming the pattern, and the available light amount is increased by the surface. I do.

Preferably, a rough surface including the specific uneven structure and an opening forming the pattern are aligned.

[0033] Preferably, it is disposed on at least one of said two contact portions (18, 20) having openings forming said pattern, and supports metal at a predetermined interval to improve adhesion. A working dielectric encapsulant (22) is included.

Preferably, said dielectric sealing material (22)
Is selected from the group comprising silicon dioxide, silicon nitride, aluminum nitride, titanium dioxide, and aluminum oxide.

Preferably, the shape of each of the openings forming the pattern is selected from a group including a circle, a square, a grid-like line, and a honeycomb.

Further, according to the method of manufacturing a light emitting device according to the present invention, a step of forming a conductive material on a heterojunction device that functions to emit visible light of wavelength λ, and a step of forming a contact portion made of the conductive material Forming an opening having the pattern so as to have a minimum width of 1 / 4λ, and allowing visible light to be emitted through the space of the opening.

Preferably, the step of forming the pattern-forming opening in the conductive material includes the step of annealing the hetero-junction device (110) and the step of forming and exposing a resist to form the pattern-forming opening. Defining a portion (120), etching the opening forming the pattern in the conductive material (130), and removing the resist (140).

Preferably, the step (130) of etching the opening forming the pattern is a step of performing ion milling on the top surface of the heterojunction device corresponding to the opening forming the pattern.

Preferably, the method further includes a step (150) of depositing a dielectric sealing material (150) on the contact portion provided with the opening forming the pattern.

Preferably, the step of forming the opening forming the pattern in the conductive material includes the step of forming the conductive material on the hetero-junction device serving to emit visible light (100); Annealing the contact made of the conductive material at an elevated temperature (110) to form the patterned opening in the material by surface tension.

[0041]

According to the light emitting device of the present invention, the light emitting device is made of a conductive material and is connected to each of the p-type layer and the n-type layer.
And at least one of the two contact portions includes an opening having a pattern having a minimum dimension of λλ, and light can be emitted through the opening. It is possible to emit uniform light with sufficient luminous intensity.

According to the method for manufacturing a light emitting device of the present invention, a step of forming a conductive material on a heterojunction device that functions to emit visible light of wavelength λ, and a step of forming a conductive portion on the contact portion made of the conductive material Forming an opening having a pattern so as to have a minimum width of λλ, and enabling emission of visible light through the space of the opening. Manufacturable.

[Brief description of the drawings]

FIG. 1 shows a first preferred embodiment of the present invention.

FIG. 2 is a flowchart showing each step of a manufacturing method according to the present invention.

FIG. 3 is a diagram comparing the light efficiency of a conventional LED using a translucent AuNi thin film with the light efficiency of the present invention.

FIG. 4 illustrates a second preferred embodiment of the present invention.

FIG. 5 illustrates a third preferred embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 heterojunction device 12 n-type layer 14 light-emitting layer 16 p-type layer 18 n-type layer contact part 20 p-type layer contact part 22 dielectric sealing material

Claims (15)

[Claims] An n-type layer, a p-type layer, and the n-type layer and the p-type layer.
A heterojunction device, which is an AlInGaN device, including a light emitting layer interposed between the mold layers and functioning to emit visible light λ, and one of which is an n-type layer contact portion connected to the n-type layer, One of which is a p-type layer contact portion connected to the p-type layer, and has two contact portions made of a conductive material, and at least one of the two contact portions has a minimum dimension of 1 /
A light emitting device comprising a 4λ pattern opening, and capable of emitting light through the opening. 2. The light emitting device according to claim 1, wherein the opening forming the pattern covers 20 to 80% of the top surface area of the p-type layer contact portion. 3. At least one of said two contact portions is 7
The light emitting device according to claim 2, wherein the light emitting device is a reflective metal having a normal incidence reflectance of more than 0%. 4. The material constituting the p-type layer contact portion is A
The light emitting device of claim 3, wherein the light emitting device is selected from the group consisting of g, Al, Rh, and an alloy of Ag, Al, and Rh. 5. The material forming the p-type layer contact portion comprises a multilayer contact portion including the reflective metal, and the reflective metal is selected from a group including Ag, Al, and Rh. The light emitting device according to claim 3, wherein: 6. The heterojunction device has a rough surface including a specific relief structure under at least one of the two contact portions having the openings forming the pattern, and a light amount usable by the surface. The light-emitting device according to claim 1, wherein? 7. The light emitting device according to claim 6, wherein a rough surface including the specific uneven structure and an opening forming the pattern are aligned. 8. The device according to claim 2, further comprising an opening defining the pattern.
7. The method of claim 3, further comprising a dielectric encapsulation material disposed on at least one of the two contacts and serving to improve adhesion by supporting the metal at predetermined intervals. The light-emitting device according to item 1. 9. The light emitting device according to claim 8, wherein said dielectric sealing material is selected from a group including silicon dioxide, silicon nitride, aluminum nitride, titanium dioxide, and aluminum oxide. 10. The light emitting device according to claim 1, wherein the shape of each of the openings forming the pattern is selected from a group including a circle, a square, a grid-like line, and a honeycomb. 11. A step of depositing a conductive material on a heterojunction device that functions to emit visible light having a wavelength of λ, and a pattern formed so that a contact made of the conductive material has a minimum width of １ ／ λ. Forming an opening that forms: and allowing visible light to emit through the space of the opening. 12. The step of forming the pattern-forming openings in the conductive material includes the steps of annealing the hetero-junction device and forming and exposing a resist to define the pattern-forming openings. The method of manufacturing a light emitting device according to claim 11, further comprising: a step of etching the opening forming the pattern in the conductive material; and removing the resist. 13. The step of etching the opening forming the pattern is a step of performing ion milling on the top surface of the heterojunction device corresponding to the opening forming the pattern. A method for manufacturing a light emitting device according to claim 12. 14. The method according to claim 11, further comprising a step of depositing a dielectric sealing material on the contact portion having the opening forming the pattern. . 15. The step of forming the pattern-forming openings in the conductive material includes the steps of: depositing the conductive material on the heterojunction device that functions to emit visible light; Annealing the contact portion made of a conductive material to form an opening forming the pattern in the material by surface tension.
3. The method for manufacturing a light emitting device according to item 1.